This invention relates to automotive vehicle mufflers and, more particularly, mufflers having means for catalytically converting polluting gases into non-polluting gases.
This invention is of great importance on the one hand because it will further automotive technology, and, on the other hand, because it will prevent the creation of photochemical pollutants.
Water and carbon dioxide or carbon anhydride are rarely harmful when compared with such components as hydrocarbons, carbon monoxide, and nitrogen-oxides. For example, on a sunny day, without air, these latter components will react in such a way that they will produce a "photochemical smog" and cause damage to the eyes and throat as well as to plants.
Photochemical smog is more bothersome than it is damaging to one's health. Nevertheless, in reality some of its components are toxic and their pollution levels in the street, when compared with what a person can medically withstand, continue to increase and will creat major problems.
The maximum permissible concentrations are shown in FIG. 1, which is a comparative table of the amount of pollutants emitted by gasoline and diesel engines and which also shows that carbon monoxide is a substance that can cause more damage and which in high concentrations can be very harmful.
In addition, the effects of long-term exposure to low concentrations of these harmful gases are not known, although it is known that toxicity affects the health and reactions of drivers and operators and therefore the health of other persons travelling along the roads and highways.
In comparing inhalations of carbon monoxide with cigarette smoke, its effect can perhaps be equally as serious. Cigarette smoke, however, is a voluntary action that may be suspended when one chooses to do so. But this is not the case with exhaust gas from automobiles, which is imposed upon people in the surrounding environment and is difficult to avoid. For this reason, more attention must be devoted to its control and elimination.
Problems arising from CO and HC (hydrocarbons) are of a different type altogether, since they affect entire areas, whereas CO is a problem of local concentration, found only at intersections with a great deal of traffic. Nevertheless, in both cases the climate has a great influence and plays a major role, as, for example, in England, the air that flows through the city greatly aids in dispersing this type of gas by rapidly removing concentrations of same.
FIG. 1 shows that lead is not a problem. Nevertheless, perhaps long-term exposure to same may affect one's health. In this connection, it has been observed year after year that lead concentrations have increased in the water and in some foods; nevertheless, it seems that up to now its admission and expulsion are balanced in the human body, at least for the time being.
Gas emissions are caused, among other reasons, by an insufficient burning, by soft burning, or by poor carburetion, i.e., any factor that causes incomplete combustion. In effect, the fuel in the gasoline is not always completely burned and, therefore, the exhaust gases contain carbon monoxide (CO) unburned hydrogen, or hydrocarbons (HC) and nitrogen oxides (NO.sub.x). On the other hand, when fuels are completely burned, the exhaust products are converted into water, carbon dioxide or carbon anhydride and small amounts of other products coming from the material of the additives.
Gasoline, in its character as the most common fuel used by vehicles, is a complex mixture of hydrocarbon compounds, which can contain more than 100 types of different compounds of same, ranging from a completely volatile element with only a few carbon atoms per molecule to very "heavy" compounds that can contain 20 or more carbon atoms per molecule.
It is important to note here the existence and use of additives in automotive vehicles. Gasoline, in fact, includes small quantities of additives, for example, lead compounds that have properties for preventing or reducing engine "knock". Other additives serve to control congestion in the carburetor.
Therefore, since hydrocarbons constitute one of the principal causes of photochemical smog, it is important to mention that when the breakdown point in the combustion stage is reached, the hydrocarbon content increases rapidly. The reason for the breakdown of the hydrocarbon content so that it drops to zero is because in an engine, part of the mixture does not have the chance to be burned, even in cases in which the richness of same is not the most desirable. In the first place, in an engine with a long valve-open period, a significant portion of the mixture passes directly to the exhaust without being trapped and further combusted in the cylinder. In the second place, all engines have, or receive a layer of a relatively cool mixture near the walls of the combustion chamber, which is not burned because the flow is smothered or flooded due to heat loss when it reaches said wall. This unburned cold layer of gas is only some thousandths of an inch thick, but is is very rich in hydrocarbons; therefore, during the exhaust period, several particles from this layer enter directly into the exhaust current by means of the depuration action originating in the chamber.
With respect to carbon monoxide, the concentration is reduced when the richness of the mixture varies from a rich condition to a lean condition. The carbon monoxide content in the exhaust gases is very small. For example, carbon monoxide concentrations (CO) in an engine at piston-deadcenter tend to be higher due to the difficulty found in burning a weak mixture under conditions of high dilution of exhaust. In addition, large emissions of gas may also be observed during acceleration periods.
It is important also to note that in practice a new complication arises, namely, high combustion temperature causing dissociation of the nitrogen in the air and the formation of nitrogen oxide and nitric oxide (NO).sub.x. There is, therefore, no time for an inverse reaction during the rapid expansion of gases in the piston stroke resulting in some nitrogen oxide appearing in the exhaust, chiefly in the form of nitric oxide. The principal factor controlling the composition of the gases is the richness of the mixture. Also, it is important to take atmospheric pressure into account.
It must also be borne in mind that there exist elements that are derived from the additives, the most important of which is lead. The anti-knock additives, namely lead, contain lead tetraethyl (TEL) or lead tetramethyl (TML), with bromide used as an adjustor. Usually, approximately one-fourth of the lead remains in the lubricating oil of the motor and in the exhaust system, while the rest is deposited rapidly by the action of the air. Nevertheless, approximately 10% leaves via the exhaust in the form of particles less than one microgram in diameter.
Nor should it be forgotten that the counter-compressions of an engine cause damage, but it is not desirable for the engine to eliminate every counter-compression.
Straight mufflers have been designed to preserve a small amount of the counter-compression, although not as much as those having dampeners, especially in the development of high r.p.m. engines. The polluting gases described heretofor are formed during combustion of gasoline or diesel fuel.
In considering the most appropriate means for controlling the gases discharged via the exhaust system, it is preferable to take a more curative than preventive approach.
The basic means is to add extra air (secondary) to the exhaust current. In addition, a catalytic converter is used to stimulate a more rapid burning of the undesirable components of the exhaust gas.
The catalytic converter which will be made with the new composition, which is the subject of this invention, will replace the conventional muffler. In the muffler of this invention the gas will pass through the catalytic component which will reduce the level of carbon monoxide (CO) to the concentration level specified in the most recent acceptable standards. The muffler will have no effect on the efficiency of the vehicle.
Most of the carbon monoxide and nitrogen oxide are released only via the exhaust pipe. However, with hydrocarbons, 60% will exhaust through the exhaust pipe, but another 20% will escape from the crankcase. The remaining 20% is lost through evaporation.
The design of automobile exhaust systems has developed into a highly complex technology. The converter, which is the subject of the invention, will greatly improve the art but still within the strict framework of limitations on space, weight, durability and cost.
Having attempted to illustrate the causes responsible for photochemical smog and the elements that constitute it, it is of particular importance to emphasize that the converter, which is the subject of this invention, has been built and successfully tested.